Optical switch

ABSTRACT

An optical switch having a plurality of switch cells. The optical switch has n inputs (n is a natural number) and m outputs (m is a natural number). The optical switch has a unit size defined as the distance between any two adjacent ones of the switch cells. The optical switch comprises a substrate having a switch size of K×L (K is an integer satisfying n≦K, and L is an integer satisfying m≦L), first and second mirrors parallel to each other and perpendicular to a principal surface of the substrate, and an optical unit providing a plurality of input optical paths for the n inputs and a plurality of output optical paths for the m outputs. The plurality of input optical paths are inclined relative to the first and second mirrors, and the plurality of output optical paths are inclined relative to the first and second mirrors. Each switch cell comprises a switch mirror provided movably relative to the substrate. With this configuration, the path dependence of loss is substantially eliminated.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application that claims the benefit of U.S. patentapplication Ser. No. 09/924,606, filed Aug. 9, 2001, now a U.S. Pat. No.6,907,154.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical switch, and moreparticularly to an optical switch suitable for a node in a photonicnetwork using wavelength division multiplexing (WDM).

2. Description of the Related Art

The development and commercialization of a wavelength divisionmultiplexing (WDM) system are proceeding as a communication system thatcan greatly increase a transmission capacity. To construct a large-scalephotonic network by connecting WDM systems, there has been examined aring type network obtained by connecting nodes through optical fibers inthe form of a loop.

In the ring type network, a transmission capacity in the loop increaseswith an increase in scale of the network. However, in each node, it issufficient to perform processing using a relatively small-scale opticalswitch.

To the contrary, in a mesh type network, a transmission capacity in eachroute is small, but it is necessary to perform processing using alarge-scale optical switch in each node.

Further, not only in the ring type network, but also in a point-to-pointlink system, an electrical switch is conventionally used to extractlower-order signals in the node. By substituting an optical switch forthe electrical switch, a cost in the node can be reduced. Accordingly,the development of a large-scale optical network is proceeding invarious types of networks.

A waveguide type optical switch is known as a conventionalcommercialized small-scale optical switch. The waveguide type opticalswitch includes a switch element and fiber arrays for inputs and outputsconnected to the switch element.

To increase the scale of the switch element, the yield of each switchcell itself formed on the switch element must be increased. However,increasing the yield is relatively difficult because of narrowmanufacturing tolerances. Further, loss is caused by a loss in eachswitch cell and losses at the connections between the input and outputfibers and the switch element.

Accordingly, in increasing the scale of the waveguide type opticalswitch, it is necessary not only to improve the yield by improving themanufacturing method, but also to remarkably improve the performance ofthe switch element.

On the other hand, a configuration of spatially switching light isconsidered as a traditional technique. By using a reflection mirror asan element for changing an optical path, the problems in performance ofthe waveguide type optical switch, such as on/off ratio and crosstalkcan be almost eliminated.

However, such a space switch is large in volume, and it is thereforedifficult to increase the scale of the switch from the viewpoint ofsize.

To break through such circumstances, there has recently been developed atechnique of reducing the size of this space switch by using asemiconductor technology. This technique is referred to as MEMS (MicroElectro Mechanical System), and it is also called optical MEMS in thecase of application to the field of optics.

The optical switch using MEMS has a plurality of small mirrors formed ona substrate by a semiconductor fabrication technique, and performsswitching of optical paths by selectively raising these mirrors bystatic electricity.

Information on MEMS may be provided by IEEE Photonic Technology Letters,Vol. 10, No. 4, April 1998, pp. 525–527.

The optical switch using MEMS is superior in switch performance to awaveguide switch owing to the use of the mirrors, and has a small sizelike the waveguide switch. However, as will be hereinafter described, anoptical path length differs according to a switching path, causing pathdependence of loss. Further, when the optical path length increases withan enlargement in scale, an increase in loss due to beam spread alsobecomes a matter of concern because of spatial coupling.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalswitch which can be reduced in size.

It is another object of the present invention to provide an opticalswitch which can eliminate path dependence of loss.

Other objects of the present invention will become apparent from thefollowing description.

In accordance with an aspect of the present invention, there is providedan optical switch having a plurality of switch cells. The optical switchhas n inputs (n is a natural number) and m outputs (m is a naturalnumber). The optical switch has a unit size defined as the distancebetween any two adjacent ones of the switch cells. The optical switchcomprises a substrate having a switch size of K×L (K is an integersatisfying n≦K, and L is an integer satisfying m≦L), first and secondmirrors parallel to each other and perpendicular to a principal surfaceof the substrate, and an optical unit providing a plurality of inputoptical paths for the n inputs and a plurality of output optical pathsfor the m outputs. The plurality of input optical paths are inclinedrelative to the first and second mirrors, and the plurality of outputoptical paths are inclined relative to the first and second mirrors.Each of the switch cells comprises a switch mirror provided movablyrelative to the substrate.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical pathswitching means arranged so as to arbitrarily guide light from aplurality of input ports to a plurality of output ports, each of theplurality of optical path switching means having a movable opticalreflecting member; and reflecting means for reflecting light from theinput ports or light from the optical reflecting members toward theoutput ports or the optical reflecting members.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical pathswitching means arranged so as to arbitrarily guide light from aplurality of input ports to a plurality of output ports, each of theplurality of optical path switching means having a movable opticalreflecting member; all the optical path lengths from the input ports tothe output ports being equal.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical pathswitching means arranged so as to arbitrarily guide light from aplurality of input ports to a plurality of output ports, each of theplurality of optical path switching meant having a movable opticalreflecting member; all the optical losses from the input ports to theoutput ports being equal.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical inputports; a plurality of optical output ports; a plurality of optical pathswitching means provided between the plurality of optical input portsand the plurality of optical output ports, each of the plurality ofoptical path switching means having a movable optical reflecting member;and reflecting means provided outside of the plurality of optical pathswitching means between the plurality of optical input ports and theplurality of optical output ports for reflecting light from the opticalinput ports or light from the optical path switching means.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical inputports; a plurality of optical output ports; a plurality of optical pathswitching means provided between the plurality of optical input portsand the plurality of optical output ports, each of the plurality ofoptical path switching means having a movable optical reflecting member;and reflecting means provided between the plurality of optical inputports and the plurality of optical output ports so as to interpose theplurality of optical path switching means for reflecting light from theoptical input ports or light from the optical path switching means.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical inputports; a plurality of optical output ports; and a plurality of opticalpath switching means provided between the plurality of optical inputports and the plurality of optical output ports, each of the pluralityof optical path switching means having a movable optical reflectingmember; optical inputs from the optical input ports to adjacent ones ofthe optical path switching means crossing each other in direction.

In accordance with another aspect of the present invention, there isprovided an optical switch comprising a plurality of optical inputports; a plurality of optical output ports; and a plurality of opticalpath switching means provided between the plurality of optical inputports and the plurality of optical output ports, each of the pluralityof optical path switching means having a movable optical reflectingmember; initial operational conditions of adjacent ones of the opticalpath switching means for receiving light from the optical input portsbeing reversed to each other.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a conventional optical switch usingMEMS;

FIG. 2 is a schematic view showing a conventional path-independentoptical switch;

FIG. 3 is a perspective view showing a preferred embodiment of theoptical switch according to the present invention;

FIGS. 4A and 4B are schematic views showing examples of path setting inthe optical switch shown in FIG. 3;

FIG. 5 is a schematic view showing a part of all examples of pathsetting in the optical switch shown in FIG. 3;

FIG. 6 is a schematic view showing the remaining part of all examples ofpath setting in the optical switch shown in FIG. 3;

FIG. 7A is a schematic view showing all switching conditions in the caseof a 3×3 optical switch, and FIG. 7B is a schematic view showing allswitching conditions in the case of a 2×2 optical switch;

FIG. 8 is a schematic view for illustrating the arrangement of switchcells in the case of an n×n optical switch;

FIG. 9 is a schematic view showing a preferred embodiment in the casethat the angle of incidence is 30°;

FIG. 10 is a schematic view showing a preferred embodiment in the casethat the angle of incidence is θi;

FIG. 11 is a schematic view for illustrating the extensibility of thepreferred embodiment according to the present invention;

FIGS. 12A and 12B are schematic views showing a 4×4 optical switch andan 8×8 optical switch (path-independent type for each) each provided asan optical waveguide, respectively;

FIG. 13A is a schematic view showing an optical switch obtained byapplying the logical configuration of the optical switch shown in FIG.12B to the present invention, and FIG. 13B is a schematic view showing apreferred embodiment for eliminating the problem in fabricationtechnique with the logical configuration shown in FIG. 13A beingmaintained;

FIGS. 14A and 14B are schematic views showing examples of the operationof the optical switches shown in FIGS. 13A and 13B, respectively;

FIG. 15 is a schematic view showing an 8×8 optical switch having aconfiguration similar to that of the 4×4 optical switch shown in FIG.13A;

FIG. 16 is a schematic view showing an 8×8 optical switch having aconfiguration similar to that of the 4×4 optical switch shown in FIG.13B;

FIGS. 17A and 17B are schematic views for illustrating the operation ofa 4×4 optical switch including spherical lenses according to the presentinvention;

FIG. 18 is a schematic view showing a part of all, or 24 kinds ofswitching conditions of the optical switch shown in FIGS. 17A and 17B;

FIG. 19 is a schematic view showing the remaining part of all, or 24kinds of switching conditions of the optical switch shown in FIGS. 17Aand 17B;

FIG. 20 is a schematic view showing all, or six kinds of switchingconditions of a 3×3 optical switch according to the present invention assimilar to the schematic views shown in FIGS. 18 and 19;

FIG. 21 is a schematic view for illustrating a general configuration ofthe optical switch according to the present invention including theconfigurations shown in FIGS. 17A, 17B, 18, 19, and 20;

FIG. 22 is a schematic view showing a 4×4 optical switch including rodlenses according to the present invention;

FIG. 23 is a schematic view showing a part of all, or 24 kinds ofswitching conditions of the optical switch shown in FIG. 22;

FIG. 24 is a schematic view showing the remaining part of all, or 24kinds of switching conditions of the optical switch shown in FIG. 22;

FIG. 25 is a schematic view showing all, or six kinds of switchingconditions of a 3×3 optical switch configured similarly to the opticalswitch shown in FIG. 22;

FIG. 26 is a schematic view showing all, or two kinds of switchingconditions of a 2×2 optical switch configured similarly to the opticalswitch shown in FIG. 22;

FIG. 27 is a schematic view showing the arrangement of switch cells androd lenses in an n×n optical switch configured as similarly to theoptical switch shown in FIG. 22;

FIG. 28 is a schematic view for illustrating the configuration andoperation of a 4×4 optical switch according to the present invention;

FIG. 29 is a schematic view showing an n×n optical switch according tothe present invention;

FIG. 30 is a schematic view for illustrating the formation of an excessspace for rod lenses in the case that the number of channels is lessthan 6;

FIG. 31 is a schematic view for illustrating the operation of the n×noptical switch (see FIG. 29) according to the present invention;

FIG. 32 is a schematic view for illustrating an improvement in theoptical switch shown in FIG. 31;

FIG. 33 is a schematic view for illustrating another improvement in theoptical switch shown in FIG. 31;

FIG. 34 is a schematic view for illustrating still another improvementin the optical switch shown in FIG. 31;

FIG. 35 is a schematic view showing an n×n optical switch according tothe present invention;

FIG. 36 is a schematic view showing all, or six kinds of switchingconditions of a 3×3 optical switch according to the present invention;

FIG. 37 is a schematic view showing all, or two kinds of switchingconditions of a 2×2 optical switch according to the present invention;

FIG. 38 is a schematic view showing a part of all, or 24 kinds ofswitching conditions of a 4×4 optical switch according to the presentinvention;

FIG. 39 is a schematic view showing another part of all, or 24 kinds ofswitching conditions of the 4×4 optical switch shown in FIG. 38;

FIG. 40 is a schematic view showing the remaining part of all, or 24kinds of switching conditions of the 4×4 optical switch shown in FIG.38;

FIG. 41 is a schematic view showing an n×n optical switch obtained byadding a plurality of rod lenses to the optical switch shown in FIG. 35;

FIG. 42 is a schematic view showing a part of all, or 24 kinds ofswitching conditions of a 4×4 optical switch according to the presentinvention;

FIG. 43 is a schematic view showing the remaining part of all, or 24kinds of switching conditions of the 4×4 optical switch shown in FIG.42;

FIG. 44 is a schematic view for summarizing the conditions shown inFIGS. 42 and 43 to clarify the directions of reflections on the mirrorsof the switch cells;

FIG. 45 is a schematic view for illustrating the kinds of the plural rodlenses;

FIG. 46 is a schematic view showing an 8×8 optical switch according tothe present invention;

FIG. 47 is a schematic view for illustrating the operation of theoptical switch shown in FIG. 46;

FIG. 48 is a schematic view for illustrating the operation of theoptical switch shown in FIG. 46;

FIG. 49 is a schematic view showing an n×n optical switch according tothe present invention;

FIG. 50 is a schematic view for illustrating the number of switch cellswith the associated equations for calculation thereof; and

FIG. 51 is a schematic view for illustrating a lens region for arranginglenses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments of the present invention will now bedescribed in detail with reference to the attached drawings.

Referring to FIG. 1, there is shown a conventional optical switch usingMEMS. This optical switch is configured so that four input channels #1to #4 and four output channels #1 to #4 are arranged in orthogonalrelationship with each other and 16 switch cells are arranged so as tooptically couple any arbitrary one of the input channels #1 to #4 to anyarbitrary one of the output channels #1 to #4. The switch cells areprovided at 4×4 lattice positions.

Each switch cell can switch optical paths by forming a small mirror on asubstrate by a semiconductor fabrication technique and driving thismirror by an electrostatic force. For example, each switch cell canswitch between a first condition where the mirror is parallel to aprincipal surface (parallel to the sheet of FIG. 1) of the substrate anda second condition where the mirror is perpendicular to the principalsurface.

This optical switch is superior in switch performance to an opticalwaveguide switch owing to the use of the mirrors, and can be reduced insize like the optical waveguide switch. However, as shown in FIG. 1, anoptical path length differs according to a switching path, causing pathdependence of loss. Further, when the optical path length increases withan enlargement in scale, an increase in loss due to beam spread alsobecomes a matter of concern because of spatial coupling.

Referring to FIG. 2, there is shown a conventional path-independentoptical switch. This optical switch is configured so that four inputchannels #1 to #4 and four output channels #1 to #4 are arrangedsubstantially parallel to each other and 16 switch cells are provided inthe form of a matrix between these input and output channels. The 16switch cells include four 1×2 switch cells, eight 2×2 switch cells, andfour 2×1 switch cells. All of the switch cells may be formedsimultaneously on a waveguide substrate.

In this optical switch, the loss between the input channels and theoutput channels is made independent of a path by properly connecting theswitch cells.

In the optical switch shown in FIG. 1, each input channel and eachoutput channel are optically coupled by one 90° reflection. Accordingly,the optical switch shown in FIG. 1 cannot obtain optical path setting asshown in FIG. 2 which can be relatively freely obtained in an opticalwaveguide. The path dependence of loss becomes fatal with an enlargementin scale of an optical switch. Therefore, in the optical switch usingreflection type switch cells as shown in FIG. 1, it is earnestly desiredto eliminate the path dependence of loss.

FIG. 3 is a perspective view of an optical switch according to thepresent invention. This optical switch includes a substrate 2 integrallyhaving 16 switch cells (optical path switching means) formed by MEMS,mirrors 4 and 6 parallel to each other and perpendicular to a principalsurface 2A of the substrate 2, and an optical unit 8 providing inputoptical paths P1 for input channels (input ports) #1 to #4 and outputoptical paths P2 for output channels (output ports) #1 to #4.

The optical unit 8 includes optical fibers 10 provided so as torespectively correspond to the input channels #1 to #4 and opticalfibers 12 provided so as to respectively correspond to the outputchannels #1 to #4. Collimating optical systems are formed by lenses (notshown) between the optical fibers 10 and the optical fibers 12. Theoptical fibers 10 are provided so that the input optical paths P1 areparallel to each other and inclined relative to the mirrors (reflectingmeans) 4 and 6. The optical fibers 12 are provided so that the outputoptical paths P2 are parallel to each other and inclined relative to themirrors 4 and 6. In this preferred embodiment, the optical fibers 10 and12 are parallel to each other on the same plane.n²

The switch cells are provided on the principal surface 2A of thesubstrate 2. Each switch cell includes a switch mirror 14 movablerelative to the substrate 2, and can switch between a first conditionwhere the switch mirror 14 is parallel to the principal surface 2A and asecond condition where the switch mirror 14 is perpendicular to theprincipal surface 2A. In this preferred embodiment, each switch mirror14 is parallel to the mirrors 4 and 6 in the second condition.

When the distance between any nearest two switch cells in this opticalswitch is defined as a unit size, the substrate 2 has a 4×4 switch size.The 16 switch cells are provided at 4×4 lattice positions. The substrate2 may have a size larger than the switch size.

With this configuration, the optical path length can be made constantregardless of a switching path to eliminate variations in loss accordingto the path as understood from the examination of various optical pathsto be hereinafter described.

Referring to FIGS. 4A and 4B, there are shown examples of path settingin the optical twitch shown in FIG. 3. FIG. 4A shows a case that theinput channels #1 to #4 are connected to the output channels #1 to #4,respectively. In this case, the switch cells in the third row, the firstcolumn, in the third row, the second column, in the second row, thethird column, and in the second row, the fourth column are in the secondcondition, and the other switch cells are in the first condition.

FIG. 4B shows a case that the input channels #1 to #4 are connected tothe output channels #4 to #1, respectively. In this case, the switchcells in the first row, the first column, in the first row, the secondcolumn, in the third row, the first column, in the third row, the fourthcolumn, in the fourth row, the second column, and in the fourth row, thefourth column are in the second condition, and the other switch cellsare in the first condition. With the configuration of the optical switchas shown in FIG. 3, an arbitrary path can be established by the fixedmirrors 4 and 6 and the switch mirror 14 of each switch cell, thusallowing the provision of a nonblocking optical switch.

FIGS. 5 and 6 show all examples of path setting in the optical switchshown in FIG. 3, and the manner of viewing the examples shown in FIGS. 5and 6 is the same as that in FIGS. 4A and 4B.

The optical switch in this case has four inputs and four outputs.Accordingly, when the unit size defined as the distance between anynearest two switch cells is 1, the switch size is 4×4. Further, when thediagonal length of each switch cell is 1, the optical path length is 4in all the examples. The number of reflections on the mirror surfaces isclassified into three kinds, i.e., 2, 4, and 0. The optical switch has16 switch cells classified into five switch cells having downward-onlyreflection mirrors (lower-sided reflection mirrors), five switch cellshaving upward-only reflection mirrors (upper-sided reflection mirrors);and six switch cells having bidirectional reflection mirrors(double-sided reflection mirrors).

Referring to FIG. 7A, there are schematically shown all switchingconditions in the case that the optical switch has three inputs andthree outputs. The switch size is 3×3, and the optical path length is 3when the diagonal length of each switch cell is 1. The number ofreflections on the mirror surfaces is classified into three kinds, i.e.,2, 4, and 0. The optical switch in this case has nine switch cellsclassified into four switch cells having downward-only reflectionmirrors, four switch cells having upward-only reflection mirrors, andone switch cell having a bidirectional reflection mirror.

Referring to FIG. 7B, there are schematically shown all switchingconditions (two switching conditions) in the case that the opticalswitch has two inputs and two outputs. In this case, the switch size is2×2, and the optical path length is 2 when the diagonal length of eachswitch cell is 1. The number of reflections on the mirror surfaces isclassified into two kinds, i.e., 2 and 1. The optical switch in thiscase has four switch cells classified into two switch cells havingdownward-only reflection mirrors and two switch cells having upward-onlyreflection mirrors.

FIG. 8 is a schematic view for illustrating the arrangement of switchcells in the case that the optical switch has n inputs and n outputs (nis an integer greater than 2). The switch size is n×n, and the opticalpath length is n when the diagonal length of each switch cell is 1. Thenumber of reflections on the mirror surfaces is classified into threekinds, i.e., 2, 4, and 0. The optical switch in this case has n² switchcells classified into (n+1) switch cells having downward-only reflectionmirrors, (n+1) switch cells having upward-only reflection mirrors, and(n²−2n−2) switch cells having bidirectional reflection mirrors.

The switch cell in the i-th row, the j-th column transmits incidentlight toward the switch cell in the (i+1)-th row, the (j+1)-th column inthe first condition, or reflects incident light toward the switch cellin the (i−1)-th row, the (j+1)-th column in the second condition.

In the above preferred embodiment, the distance between any adjacent twoswitch cells arranged along each row is equal to the distance betweenany adjacent two switch cells arranged along each column, and the angleof incidence (the angle formed between the axis of an incident beam andeach mirror surface) is 45°. However, the present invention is notlimited to the configuration that the angle of incidence is 45°.

For example, the angle of incidence may be 30° as shown in FIG. 9. Inthis case, the distance between any adjacent two switch cells arrangedalong each row may be set twice the distance between any adjacent twoswitch cells arranged along each column.

Further, in the case that the angle of incidence is an arbitrary angle(θi) as shown in FIG. 10, the ratio of the distance between any adjacenttwo switch cells arranged along each row to the distance between anyadjacent two switch cells arranged along each column may be set to1:tan(θi).

Further, the distance dm between each switch cell in the first row andthe mirror 4 is expressed as d_(m)=(½)×a×tan(θ_(i)) where a is thedistance between any adjacent two switch cells arranged along each row.

The optical switch according to the present invention has extensibility.For example, by using four substrates 2 each for the optical switchhaving four inputs and four outputs as shown in FIG. 3, an opticalswitch having eight inputs and eight outputs can be obtained.

As shown in FIG. 11, such an 8×8 optical switch can be obtained byarranging four 4×4 substrates 2 so as to form a square substrate andinterposing this square substrate between common mirrors 4 and 6.

While each switch cell is configured by using MEMS in the abovepreferred embodiment, a reflection type optical switch using a fluid mayalso be used. This reflection type optical switch is configured byenclosing a bubble-bearing liquid in a cavity formed in a solid having acertain refractive index and allowing the bubble to be moved by using aheater or the like. The refractive index of the liquid is setsubstantially equal to the refractive index of the solid. Accordingly,by setting an optical path extending through the cavity, the opticalswitch can switch between transmission and total reflection according tothe presence or absence of the bubble.

Referring to FIGS. 12A and 12B, there are shown a 4×4 optical switch andan 8×8 optical switch each provided as an optical waveguide,respectively. Each optical switch is of a path-independent type.

Each switch cell switches between a cross condition corresponding to thefirst condition and a bar condition corresponding to the secondcondition in the present invention. The numeral such as (13) or (23)shown in the circle representing each switch cell relates an input to anoutput. For example, the numeral (13) means a switch element forconnecting an input channel #1 to an output channel #3. Further, eachswitch element maintains the cross condition in an electrically offcondition, and changes to the bar condition when it is electricallyturned on.

FIG. 13A shows an optical switch obtained by applying the logicalconfiguration of the optical switch shown in FIG. 12A to the presentinvention. More specifically, the odd-numbered channels andeven-numbered channels of input optical paths cross each other, and theodd-numbered channels and even-numbered channels of output optical pathscross each other.

In an optical waveguide of LN (LiNbO₃), for example, the presence ofsuch crossings does not especially cause a problem in fabricationtechnique. However, in the case of providing the input optical paths andthe output optical paths by using optical fiber arrays or the like, thecrossing of the channels may be sometimes difficult in fabricationtechnique. FIG. 13B shows an optical switch which can eliminate theabove problem in fabrication technique with the logical configurationshown in FIG. 13A being maintained.

As shown in FIG. 13B, the input optical paths are parallel to each otherand the output optical paths are also parallel to each other. Byinverting the logic in the input switch cells of the odd-numberedchannels and the logic in the output switch cells of the odd-numberedchannels or by inverting the logic in the input switch cells of theeven-numbered channels and the logic in the output switch cells of theeven-numbered channels, light is normally reflected by each switch cell,and in the case that each switch cell is made active to establish apath, light is not reflected by each switch cell.

In each of FIGS. 13A and 13B, the number of upward reflecting switchcells is 8 and the number of downward reflecting switch cells is 8.Further, the number of reflections on the mirror surfaces of the switchcells in FIG. 13A is classified into three kinds, i.e., 1, 2, and 3, andthe number of reflections on the mirror surfaces of the switch cells inFIG. 13B is classified into three kinds, i.e., 0, 2, and 4.

In the configuration of FIG. 13A, each switch mirror is normally in thefirst condition, and in the case that each switch mirror is made activeto establish a path, each switch mirror becomes the second condition. Inthe configuration of FIG. 13B, the switch cells enclosed by the circlesare normally in the second condition, and become the first conditionwhen establishing paths. The other switch cells are the same as thoseshown in FIG. 13A.

FIGS. 14A and 14B show examples of the operation of the optical switchesshown in FIGS. 13A and 13B, respectively, and FIGS. 15 and 16 show 8×8optical switches having configurations similar to the configurations ofthe 4×4 optical switches shown in FIGS. 13A and 13B, respectively.

According to the present invention as described above, it is possible toprovide a path-independent, nonblocking optical switch.

In an optical switch using optical MEMS, there is a possibility that anoptical beam may spread to increase loss with an increase in opticalpath length because of spatial coupling between an input and an output.According to the present invention, the optical beam can be converged atan intermediate position on an optical path. This configuration willfirst be described in the case of a 4×4 optical switch with reference toFIGS. 17A and 17B.

FIGS. 17A and 17B are schematic views for illustrating the operation ofa 4×4 optical switch including spherical lenses according to the presentinvention. When the size of each switch cell 1, the switch size of thisoptical switch is 4×5, and when the diagonal length of each switch cellis 1, the optical path length in this optical switch is 5. In thisexample, four spherical lenses are provided in the third column.

In the condition shown in FIG. 17A, the input channels #1 to #4 areconnected to the output channels #1 to #4, respectively. In thecondition shown in FIG. 17B, the input channels #1 to #4 are connectedto the output channels #4 to #1, respectively.

FIGS. 18 and 19 are schematic views showing all switching conditions (24kinds of switching conditions) of the optical switch shown in FIGS. 17Aand 17B. The number of switch cells is 16, and these 16 switch cells areclassified into four switch cells having downward-only reflectionmirrors, four switch cells having upward-only reflection mirrors, andeight switch cells having bidirectional reflection mirrors. Five ones ofthe eight switch cells having bidirectional reflection mirrors performsimultaneous bidirectional reflection. If each bidirectional reflectionmirror is thick in this case, it is difficult to simultaneously reflecttwo incident beams at a given reflection point. Accordingly, it isdesirable to reduce the thickness of each reflection mirror according tothe scale of the optical switch.

FIG. 20 is a schematic view showing all switching conditions (six kindsof switching conditions) of a 3×3 optical switch according to thepresent invention as similar to the schematic views shown in FIGS. 18and 19. The switch size is 3×4 when the size of each switch cell is 1,and the optical path length is 4 when the diagonal length of each switchcell is 1. The number of reflections on the mirror surfaces isclassified into two kinds, i.e., 2 and 4. The number of switch cells is9, and these nine switch cells are classified into three switch cellshaving downward-only-reflection mirrors, three switch cells havingupward-only reflection mirrors, and three switch cells havingbidirectional reflection mirrors.

FIG. 21 is a schematic view for illustrating a general configuration ofthe optical switch according to the present invention including theconfigurations shown in FIGS. 17A, 17B, 18, 19, and 20. That is, FIG. 21shows the arrangement of switch cells and spherical lenses in an n×noptical switches (n is an integer greater than 2).

When n is an even number, the optical switch has n lenses arranged inthe (n/2+1)-th column, whereas when n is an odd number, the opticalswitch has n lenses arranged in the [(n+1)/2+1]-th column. FIG. 21 showsthe case where n is an even number.

The switch size is n×(n+1) when the size of each switch cell is 1, andthe optical path length is (n+1) when the diagonal length of each switchcell is 1. The number of reflections on the mirror surfaces isclassified into three kinds, i.e., 2, 4, and 6, or any two kindsselected from these three kinds. The number of switch cells is n², andthese n² switch cells are classified into n switch cells havingdownward-only reflection mirrors (in the first column), n switch cellshaving upward-only reflection mirrors (in the n-th column), and (n²−2n)switch cells having bidirectional reflection mirrors (in the othercolumns).

In the case that n is an even number, the optical path length on theinput side of each spherical lens is equal to that on the output side ofeach spherical lens, so that a lens optical system can be easilydesigned.

There will now be described an optical switch according to the presentinvention to which rod lenses are applicable. In the preferredembodiment described with reference to FIGS. 17A, 17B, and 18 to 21, atmost two optical paths having different directions pass through eachlens. Therefore, it is necessary to use lenses having no anisotropy suchas spherical lenses. To the contrary, the following preferred embodimentis configured so that at most one optical path passes through each lens,thereby facilitating lens mounting and optical axis alignment. Ingeneral, the tolerance of alignment of rod lenses is wider than that ofspherical lenses.

FIG. 22 shows a 4×4 optical switch including rod lenses according to thepresent invention. The switch size is 5×6 when the size of each switchcell is 1, and the optical path length is 6 when the diagonal length ofeach switch cell is 1. Eight rod lenses are provided on the substrate 2(not shown in FIG. 22, but see FIG. 3) formed with the switch cells. Therod lenses are zigzag arranged along a diagonal line of the substrate 2.

The number of switch cells is 20, and these 20 switch cells areclassified into six switch cells having downward-only reflectionmirrors, six switch cells having upward-only reflection mirrors, andeight switch cells having bidirectional reflection mirrors. In thispreferred embodiment, it is not necessary to provide any simultaneousbidirectional reflection mirrors. The number of reflections on themirror surfaces is classified into two kinds, i.e., 2 and 4. The eightrod lenses are arranged in the second to fifth columns so that every tworod lenses are arranged obliquely in parallel to each other in the samecolumn. In the case that the input optical paths and the output opticalpaths are pointed upward to the right, each rod lens is pointed downwardto the right.

FIGS. 23 and 24 are schematic views showing all switching conditions (24kinds of switching conditions) of the optical switch shown in FIG. 22.

FIG. 25 is a schematic view showing all switching conditions (six kindsof switching conditions) of a 3×3 optical switch configured similarly tothe optical switch shown in FIG. 22. In the optical switch shown in FIG.25, the switch size is 4×5 when the size of each switch cell is 1, andthe optical path length is 5 when the diagonal length of each switchcell is 1. The number of reflections on the mirror surfaces isclassified into two kinds, i.e., 2 and 4. The number of switch cells is12, and these 12 switch cells are classified into five switch cellshaving downward-only reflection mirrors, five switch cells havingupward-only reflection mirrors, and two switch cells havingbidirectional reflection mirrors. In some switching conditions shown inFIG. 25, no rod lenses are shown, but a region where the rod lenses arepresent is shown.

FIG. 26 is a schematic view showing all switching conditions (two kindsof switching conditions) of a 2×2 optical switch configured similarly tothe optical switch shown in FIG. 22. The switch size is 3×4 when thesize of each switch cell is 1, and the optical path length is 4 when thediagonal length of each switch cell is 1. The number of reflections onthe mirror surfaces is always 2. The number of switch cells is 6, andthese six switch cells are classified into three switch cells havingdownward-only reflection mirrors and three switch cells havingupward-only reflection mirrors.

FIG. 27 is a schematic view showing the arrangement of switch cells androd lenses in an n×n optical switch configured similarly to the opticalswitch shown in FIG. 22. The switch size is (n+1)×(n+2) when the size ofeach switch cell is 1, and the optical path length is (n+2) when thesize of each switch cell is 1. While the optical path length from aninput to a rod lens and the optical path length from the rod lens to anoutput are different according to the column where the rod lens ispositioned, the number of kinds of the rod lenses is about (n/2), whichwill be hereinafter discussed. The positions of the rod lenses areexpressed in (row, column) as (1, n+1), (2, n), (2, n+1), . . . , (i,n−i+2), (i, n−i+3), . . . , (n, 2), (n, 3), and (n+1, 2).

The number of reflections on the mirror surfaces is classified into twokinds, i.e., 2 and 4.

The number of switch cells is n×(n+1). Of these n×(n+1) switch cells,the number of switch cells having downward-only reflection mirrors is 3when n=2, 5 when n=3, or (2n−2) when n>3. The number of switch cellshaving upward-only reflection mirrors is the same as the number ofswitch cells having downward-only reflection mirrors. The number ofswitch cells having bidirectional reflection mirrors is 0 when n=2, 2when n=3, or (n²−3n+4) when n>3.

In the above preferred embodiments, the path depends on the number ofmirror reflections inclusive of the reflection on the mirror 4 or 6. Inthe case that reflection loss is not negligible, the path dependence ofloss is generated according to the number of reflections. In thefollowing preferred embodiments, the number of reflections is fixed to 2in order to eliminate the path dependence of loss.

FIG. 28 is a schematic view for illustrating the configuration andoperation of a 4×4 optical switch according to the present invention.Four switch cells are arranged in the first column on the input side,and an optical signal from each switch cell in the first column isswitched by specific switch cells. The numerals shown in the circlesrepresenting all the switch cells mean input channel numbers. Fivespecific switch cells are allocated to each input channel, so that theoptical signal is output after always two reflections withoutcongestion.

The switch size is 6×6 when the size of each switch cell is 1, and theoptical path length is 6 when the diagonal length of each switch cellis 1. This optical switch is characterized in that the number ofreflections on the mirror surfaces is always 2. The number of switchcells is 19, and these 19 switch cells are classified into four switchcells having downward-only reflection mirrors and 15 switch cells havingupward-only reflection mirrors.

FIG. 29 is a schematic view showing an n×n optical switch according tothe present invention. In FIG. 29, an 8×8 optical switch as an exampleis shown. In the first column of the n×n optical switch, n switch cellsfor downward-only reflection are arranged. Each switch cell functions todivide an input channel into two optical paths. One of the two opticalpaths is provided by the first condition of each switch cell, andincludes the reflection on the mirror 4. The other optical path isprovided by the second condition of each switch cell, and does notinclude the reflection on the mirror 4. Further, (n²−1) switch cells forupward-only reflection are provided so that the optical paths from the nswitch cells in the first column are coupled to the (n²−1) switch cells.Each switch cell for upward-only reflection is positioned so as tocorrespond to each signal optical path, and determines a final opticalpath reaching an output.

The switch size is 2(n−1)×2(n−1) when the size of each switch cell is 1,and the optical path length is 2(n−1) when the diagonal length of eachswitch cell is 1. The number of all switch cells is (n²+n−1). It is notnecessary to provide any switch cells having bidirectional reflectionmirrors.

While the number of reflections on the mirror surfaces is always 2, theoptical path length is prone to increase. Accordingly, it is preferableto provide a rod lens along each optical path. As shown in FIG. 29,there is a space between the switch cells for downward-only reflectionand the switch cells for upward-only reflection, and rod lenses may beprovided in this space.

However, in the case that the number of channels is 5 or less, such aspace for providing rod lenses is not present. Accordingly, it ispreferable to define the rod lens space by adding one row and one columnas shown in FIG. 30.

In the configuration of FIG. 29, the size of the rod lens space is(n/2−2), and in the case that n is 6 or more, the size of the rod lensspace becomes 1 or more.

The positions of the switch cells are expressed in (row, column) asfollows:

For the switch cells having downward-only reflection mirrors:

(i, 1); i=1 to n

For the switch cells having upward-only reflection mirrors:

(n/2+i, 2(n−1)−n/2+1−i); i=0 to (n−1)

(n/2+i, 2(n−1)−n/2+2−i); i=0 to (n−1)

(n/2+i+1, 2(n−1)−n/2+1−i); i=0 to (n−1)

(n−1+i, 2(n−1)−i); i=0 to (n−1)

(n+i, 2(n−1)−i); i=0 to (n−1)

The operation of the n×n optical switch (see FIG. 29) according to thepresent invention will now be described with reference to FIG. 31.First, the optical path from each switch cell in the first column isswitched according to whether the output channel is an even-numberedchannel or an odd-numbered channel. In the case that the output channelis an odd-numbered channel, the switch mirror of the switch cell in thefirst column corresponding to the input channel #2, for example, israised (set to the second condition) to switch the input optical path toan optical path along a diagonal line extending from the left uppercorner of the substrate 2 to the right lower corner thereof. In the casethat the output channel is an even-numbered channel, the switch mirrorof the switch cell is not raised (set to the first condition) to changethe input optical path by the fixed mirror 4 provided on the upper sideas viewed in FIG. 31.

Then, a final output channel is determined by a group of switch cellsarranged along a diagonal line extending from the right upper corner ofthe substrate 2 to the left lower corner thereof. In FIG. 31, the switchcell shown by (i_(n)) represents a switch cell whose switch mirror israised when the input channel is #i and the output channel is #n.

The switch size of this optical switch will now be examined. Assumingthat the input channel is #n and the output channel is an even-numberedchannel, an optical signal from the switch cell corresponding to theinput channel #n is reflected on the fixed mirror 4 at a reflectionpoint Rn, and is next input into the switch cells shown by n₂, n₄, . . ., n_(n). When the group of switch cells for upward-only reflection islocated not apart from the mirror 4 as shown, a part of the light beamis output from a position corresponding to the mirror 4 rather than froma side surface of the substrate 2, resulting in difficulty of handling.In FIG. 31, the output channels #1 to #4 are arranged at a positioncorresponding to the mirror 4.

FIG. 32 shows an improvement in the arrangement of the switch cellsshown by n₂, n₄, . . . , n_(n) such that the output channel #1 ispositioned at the right upper corner of the substrate 2. In this case,the size of each side of the substrate 2 is n+2(n/2−1)=2n−2, so that theswitch size is (2n−2)×(2n−2). In this configuration, the output channel#n is provided by an optical path produced at a reflection point on thelower mirror 6 corresponding to the switch cell shown by n_(n)−1.

The number of all switch cells is (n²+n−1), in which the number of thedownward reflection switch cells (the switch cells in the first column)is n and the number of the upward reflection switch cells (the group ofswitch cells arranged along the diagonal line extending from the rightupper corner to the left lower corner of the substrate 2) is (n²−1). Thenumber of reflections is always 2 regardless of the optical paths. Theoptical path length is (2n−2) when the diagonal length of each switchcell is 1.

FIGS. 33 and 34 show modifications of the configuration shown in FIG.32, in which the upward reflection switch cells corresponding to theoutput channels are changed in position. In the configuration of FIG.33, the upward reflection switch cells corresponding to the odd-numberedoutput channels are arranged at right upper positions, and the upwardreflection switch cells corresponding to the even-numbered outputchannels are arranged at left lower positions. On the other hand, in theconfiguration of FIG. 34, the upward reflection switch cellscorresponding to the even-numbered output channels are arranged at rightupper positions, and the upward reflection switch cells corresponding tothe odd-numbered output channels are arranged at left lower positions.

In each case, the number of all switch cells is (n²+n), in which thenumber of the downward reflection switch cells (the switch cells in thefirst column) is n, and the number of the upward reflection switch cells(the group of switch cells arranged along the diagonal line extendingfrom the right upper corner to the left lower corner of the substrate 2)is n².

The switch size of the optical switch shown in FIG. 33 is (2n−1)×(2n−1),and the optical path length is (2n−1) when the diagonal length of eachswitch cell is 1. The switch size of the optical switch shown in FIG. 34is 2n×2n, and the optical path length is 2n.

In each case, the number of reflections is 2, and the path dependence ofloss according to the number of reflections can be eliminated. As aresult, it is possible to use mirrors whose reflection loss is not low.

Further, in each of the preferred embodiments shown in FIGS. 33 and 34,it is not necessary to provide a lower mirror (the mirror 6 in theprevious preferred embodiments), thereby facilitating the manufacture ofthe optical switch.

There will now be described another preferred embodiment eliminating thepath dependence of loss according to the number of mirror reflectionslike the above preferred embodiments shown in FIGS. 28 to 34.

FIG. 35 shows an n×n optical switch according to the present invention.A plurality of switch cells are arranged in the form of an (n+1)×(n+1)lattice. It is not necessary to provide switch cells at the positions of((n+1), 1), ((n+1), (n+1)), and (1, n) expressed in (row, column), sothat the number of all switch cells is (n²+2n−2).

The switch size is (n+1)×(n+1), and the optical path length is (n+1)when the diagonal length of each switch cell is 1. The number of mirrorreflections is always 2 regardless of the optical paths.

The number of switch cells having downward-only reflection mirrors isn(n+1)/2−1, and the number of switch cells having upward-only reflectionmirrors is n(n+1)/2−1+n. In this preferred embodiment, it is notnecessary to provide switch cells having bidirectional reflectionmirrors.

FIG. 36 is a schematic view showing all switching conditions (six kindsof switching conditions) of a 3×3 optical switch according to thepresent invention. In each switching condition, the number ofreflections is 2.

The switch size is 4×4 when the size of each switch cell is 1, and theoptical path length is 4 when the diagonal length of each switch cellis 1. The number of switch cells is 13, and these 13 switch cells areclassified into five switch cells having downward-only reflectionmirrors and eight switch cells having upward-only reflection mirrors. Itis not necessary to provide switch cells having bidirectional reflectionmirrors.

FIG. 37 is a schematic view showing all switching conditions (two kindsof switching conditions) of a 2×2 optical switch according to thepresent invention. The switch size is 3×3 when the size of each switchcell is 1, and the optical path length is 3 when the diagonal length ofeach switch cell is 1.

The number of reflections on the mirror surfaces is always 2. The numberof switch cells is 6, and these six switch cells are classified into twoswitch cells having downward-only reflection mirrors and four switchcells having upward-only reflection mirrors. It is not necessary toprovide switch cells having bidirectional reflection mirrors.

FIGS. 38 to 40 show all switching conditions (24 kinds of switchingconditions) of a 4×4 optical switch according to the present invention.The switch size is 5×5 when the size of each switch cell is 1, and theoptical path length is 5 when the diagonal length of each switch cellis 1. The number of reflections on the mirror surfaces is always 2. Thenumber of switch cells is 22, and these 22 switch cells are classifiedinto nine switch cells having downward-only reflection mirrors and 13switch cells having upward-only reflection mirrors. It is not necessaryto provide switch cells having bidirectional reflection mirrors.

FIG. 41 shows an n×n optical switch obtained by adding a plurality ofrod lenses to the configuration shown in FIG. 35. In the case thatoptical MEMS is adopted, there is a possibility that although acollimator lens is provided at each of the input fiber end and theoutput fiber end, the light beam may spread with an increase in opticalpath length, causing an increase in loss. To cope with this problem, itis effective to provide a rod lens that is easy to handle along eachoptical path in the optical switch.

In the preferred embodiment shown in FIG. 41, a plurality of switchcells are arranged in the form of an (n+2)×(n+2) square lattice, and aspace for providing a plurality of rod lenses are defined along adiagonal line extending from the right upper corner to the left lowercorner of the substrate 2.

The switch size is (n+2)×(n+2) when the size of each switch cell is 1,and the optical path length is (n+2) when the diagonal length of eachswitch cell is 1.

The number of all rod lenses is 2n, and the number of kinds of the rodlenses is n/2 (which will be hereinafter described in detail).

The number of all switch cells is (n²+2n−2), in which the number ofswitch cells having downward-only reflection mirrors is (n+1)/2−1, andthe number of switch cells having upward-only reflection mirrors isn(n+2)/2−1+n. It is not necessary to provide switch cells havingbidirectional reflection mirrors. The number of mirror reflections isalways 2 regardless of the optical paths.

The positions of the rod lenses are expressed as (1, n+1), (2, n), (2,n+1), . . . , (i, n−i+2), (i, n−i+3), . . . , (n, 2), (n, 3), and (n+1,2).

FIGS. 42 and 43 show all switching conditions (24 kinds of switchingconditions) of a 4×4 optical switch according to the present invention.FIG. 44 is a schematic view for summarizing the conditions shown inFIGS. 42 and 43 to clarify the directions of reflection on the mirrorsof the switch cells.

The switch size is 6×6 when the size of each switch cell is 1, and theoptical path length is 6 when the diagonal length of each switch cellis 1. The number of reflections on the mirror surfaces is always 2.

The number of switch cells is 22, and these 22 switch cells areclassified into nine switch cells having downward-only reflectionmirrors and 13 switch cells having upward-only reflection mirrors. It isnot necessary to provide switch cells having bidirectional reflectionmirrors.

The kinds of the plural rod lenses will now be examined with referenceto FIG. 45. Four rod lenses are arranged along optical paths provided byfour collimating systems extending from four inputs to four outputs,respectively. The numbers of 1 to 4 shown in the rectangles representingthe rod lenses are intended to distinguish the rod lenses.

In each channel, the optical path length is 5 when the diagonal lengthof each switch cell is 1. For example, in the channel #1, the ratio ofthe distance between the input fiber and the rod lens to the distancebetween the output fiber and the rod lens is 1:4. Similarly, the aboveratios in the channels #2, #3, and #4 are 2:3, 3:2, and 4:1,respectively. Accordingly, the number of kinds of the rod lenses inrelation to a focal length or the like is 2. In general, the number ofkinds of rod lenses required in an n×n optical switch is n/2.

FIG. 46 shows an 8×8 optical switch according to the present invention.This optical switch is a nonblocking optical switch in which the numberof reflections is always 2 regardless of the optical paths as in theprevious preferred embodiments. The operation of this optical switchwill now be described with reference to FIGS. 47 and 48.

First, consider the case that the input channels are even-numberedchannels and the output channels are even-numbered channels as shown inFIG. 47. The broken lines in FIG. 47 show routes formed by connectingthe odd-numbered input channels to the even-numbered output channels.These routes are dedicated routes respectively corresponding to theodd-numbered input channels, and are reflected on the mirror 4. Thesolid lines in FIG. 47 show routes formed by connecting theeven-numbered input channels to the even-numbered output channels. Theseroutes are classified as follows:

(a) Three routes allowed to reach the output channels #2, #4, #6, and #8(routes (1), (2), and (3) shown in FIG. 47). Route (1) is also a routededicated to the input channel #1.

(b) One route allowed to reach the output channels #2, #4, and #6 (route(4) shown in FIG. 47).

(c) One route allowed to reach the output channels #2 and #4 (route (5)shown in FIG. 47).

(d) One route allowed to reach the output channel #2 only (route (6)shown in FIG. 47).

The allowed routes are summarized according to the even-numbered inputchannels in Table shown at a lower portion of FIG. 47. In consideringthat the most congestive routes are routes from the input channel #8 tothe output channel #8, from the input channel #6 to the output channel#6, from the input channel #4 to the output channel #4, and from theinput channel #2 to the output channel #2, it is understood that thethree routes allowed to reach the output channels #2, #4, #6, and #8 aresufficient.

Accordingly, it is sufficient to arrange the switch cells so that theroutes (1), (2), and (3) can be used.

Although the route (1) is also a route dedicated to the input channel#1, the even-numbered output channels are allocated to the even-numberedinput channels, and the route (1) is therefore not necessary.Accordingly, the route (1) may be used for the even-numbered inputchannels.

With this arrangement of the switch cells, the switch size becomes 11×11by upward increasing one row and downward increasing two rows.

Next, consider the case that the input channels are odd-numberedchannels and the output channels are odd-numbered channels as shown inFIG. 48. The broken lines in FIG. 48 show routes formed by connectingthe even-numbered input channels to the odd-numbered output channels.These routes are dedicated routes respectively corresponding to theeven-numbered input channels, and are reflected on the mirror 4.

The solid lines in FIG. 48 show routes formed by connecting theodd-numbered input channels to the odd-numbered output channels. Theseroutes are five routes. As understood from Table shown at a lowerportion of FIG. 48, it is sufficient to ensure two routes allowed toreach the output channels #1, #3, #5, and #7. This two routes areautomatically attained by setting the routes connecting theeven-numbered input channels to the even-numbered output channels.Accordingly, the switch size can be easily examined.

There will now be considered an n×n optical switch according to thepresent invention. The most important point is how many routes allowedto lead from the input channel #2 to the output channel #n are required.As understood from FIG. 49, the number of these required routes is(n/4+1). In the case that n is not a multiple of 4, (n−2) may besubstituted for n.

The size of a square lattice forming this optical switch (the length ofeach side of the square lattice) required to obtain the above number ofrequired routes is n+(n/4−1)+(n/4)=(1.5n−1) as apparent from FIG. 49.When n is large, this size becomes substantially equal to 1.5n.Accordingly, this configuration will be hereinafter referred to as “1.5nsquare lattice”.

The (n+1) square lattice type shown in FIG. 35, for example, correspondsto the case where n is 6 or less in the 1.5n square lattice type. Thenumber of switch cells will now be considered.

As understood from the equations in FIG. 50, the number of switch cellshaving upward-only reflection mirrors is (3n²/4+n/2−1), and the numberof switch cells having downward-only reflection mirrors is (n²/2).Accordingly, the number of all switch cells is (5n²/4+n/2−1).

A space for arranging beam condensing means such as rod lenses in theoptical switch is defined when n is 8 or more. In this case, the numberof lenses is (5n/2−2).

In the case that n is a multiple of 4 in the preferred embodiment shownin FIG. 49, the switch size is (3n/2−1)×(3n/2−1), and in the case that nis not a multiple of 4, the switch size is (3n/2−2)×(3n/2−2). The switchsize is larger by (n/2−1) than the switch size of n×n.

Table 1 shows the relation among the number of input and outputchannels, the number of routes from the input channel #2 to the outputchannel #n, the size increase, and the switch size in the preferredembodiment shown in FIG. 49, for example.

TABLE 1 Number of input and 4 × 4 6 × 6 8 × 8 10 × 10 12 × 12 14 × 14 16× 16 18 × 18 20 × 20 output channels Number of routes from  2  2  3  3 4  4  5  5 10 input channel #2 to output channel #n Size increase +1 +1+3 +3 +5 +5 +7 +7 +9 Switch size 5 × 5 7 × 7 11 × 11 13 × 13 17 × 17 19× 19 23 × 23 25 × 25 29 × 29

While the mirrors 4 and 6 are used as fixed mirrors, switch cells may bepositioned on the reflection points according to another preferredembodiment of the present invention. Further, while n is an even numberin an n×n optical switch in the above description, a similar functioncan be obtained also in the case that n is an odd number.

In the case that n is 8 or more, a lens region for arranging beamcondensing means such as rod lenses is defined on the substrate 2 asshown in FIG. 51. As apparent from FIG. 51, the number of lenses is(5n/2−2).

The configurations of the various preferred embodiments of the presentinvention are compared in Table 2 and 3.

According to the present invention as described above, it is possible toprovide an optical switch which can be reduced in size and can eliminatepath dependence of loss.

The effects obtained by the specific preferred embodiments of thepresent invention have been described above, so that the descriptionthereof will be omitted herein.

The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

TABLE 2 Square lattice Square lattice Square lattice Square lattice withSquare lattice with basic type A type B type spherical lenses type rodlenses type Number of input 4 × 4 n × n 4 × 4 n × n 4 × 4 n × n 4 × 4 n× n 4 × 4 n × n and output channels Size 4 × 4 n × n 4 × 4 n × n 4 × 4 n× n 4 × 5 n × (n + 1) 5 × 6 (n + 1) × (n + 2) Number of switch cells 16  n² 16   n² 16   n² 16   n² 20  n × (n + 1) Optical path length 4 n 4 n4 n 5 n + 1 6 n + 2 Number of reflections 2 or 4 2 or 4 1 or 3 1 or 3 0or 2 0 or 2 2 or 4 2 or 4 or 6 2 or 4 2 or 4 or 1 or 1 or 4 or 4 or 6Kinds of Upward 5 n + 1 8 n²/2 8 n²/2 4 n 6 2n − 2 switch reflectionmirrors Downward 5 n + 1 8 n²/2 8 n²/2 4 n 6 2n − 2 reflectionBidirectional 6 n² − 2n − 2 — — — — 8 n² − 2n 8 n² − 3n + 4 reflectionSimultaneous — — — — — — 5 all — — bidirectional reflection InsertionLens type — — — — — — Spherical Spherical Rod Rod of lenses lens lenslens lens Number of — — — — — — 4 n 8 2n lenses Remarks *1 *2 *3 *1:Blocking *2: Input optical paths of odd and even channels are crossed,and optical paths of odd and even channels are crossed. Nonblocking *3:Switch logic in the first column and the N-th column for odd channels isinverted. Nonblocking

TABLE 3 V-shaped (n + 1) (n + 1) square lattice 1.5n arranged typesquare lattice type with rod lenses type square lattice type Number ofinput 4 × 4 n × n 4 × 4 n × n 4 × 4 n × n 4 × 4 n × n and outputchannels size 6 × 6 2(n − 1) 5 × 5 (n + 1) × (n + 1) 6 × 6 (n + 2) ×(n + 2) 5 × 5 (1.5n − 1) × (1.5n − 1) Number of switch cells 19  n² + n− 1 22  n² + 2n − 2 22  n² + 2n − 2 22  1.25n² + 0.5n − 1 Optical pathlength 6 2(n − 1) 5 n + 1 6 n + 2 5 1.5n − 1 Number of reflections 2 2 22 2 2 2 2 Kinds of Upward 15  n² − 1 13  n(n + 1)/2 − 1 + n 13  n(n +1)/2 − 1 + n 13  0.75n² + 0.5n − 1 switch reflection mirrors Downward 4n 9 n(n + 1)/2 − 1 9 n(n + 1)/2 − 1 9 0.5n² reflection Birdirectional —— — — — — — — reflection Simultaneous — — — — — — — — birdirectionalreflection Insertion Lens type — Rod — — Rod Rod lens — Rod lens oflenses lens lens Number of 2n — — 8 2n — 2.5n − 2 lenses Remarks *4 *5*6 *4: In the case of n > 5, rod lenses can be inserted. Nonblocking *5:Corresponding to the case where n is 6 or less in the 1.5n squarelattice type. Blocking *6: In the case that n > 8, rod lenses can beinserted. Blocking

1. An optical switch having a plurality of switch cells, wherein: saidoptical switch has n inputs (n is a natural number) and m outputs (m isa natural number); said optical switch has a unit size defined as thedistance between any two adjacent ones of said switch cells; saidoptical switch comprises: a substrate having a switch size of K×L (K isan integer satisfying n≦K, and L is an integer satisfying m≦L), where Kand L represent a number of rows and a number of columns, respectively,of said optical switch; first and second mirrors parallel to each otherand perpendicular to a principal surface of said substrate; and anoptical unit providing a plurality of input optical paths for said ninputs and a plurality of output optical paths for said m outputs, saidplurality of input optical paths being inclined relative to said firstand second mirrors, said plurality of output optical paths beinginclined relative to said first and second mirrors; and each of saidswitch cells comprises a switch mirror provided movably relative to saidsubstrate, wherein each switch cell switches between a first conditionwhere said switch mirror is parallel to said principal surface of saidsubstrate and a second condition where said switch mirror isperpendicular to said principal surface of said substrate, and saidplurality of switch cells, said first and second mirrors, and saidoptical unit are arranged so that path lengths from said inputs to saidoutputs are equal.
 2. An optical switch having a plurality of switchcells, wherein: said optical switch has n inputs (n is a natural number)and m outputs (m is a natural number); said optical switch has a unitsize defined as the distance between any two adjacent ones of saidswitch cells; said optical switch comprises: a substrate having a switchsize of K×L (K is an integer satisfying n≦K, and L is an integersatisfying m≦L), where K and L represent a number of rows and a numberof columns, respectively, of said optical switch; first and secondmirrors parallel to each other and perpendicular to a principal surfaceof said substrate; and an optical unit providing a plurality of inputoptical paths for said n inputs and a plurality of output optical pathsfor said m outputs, said plurality of input optical paths being inclinedrelative to said first and second mirrors, said plurality of outputoptical paths being inclined relative to said first and second mirrors;and each of said switch cells comprises a switch mirror provided movablyrelative to said substrate, wherein: said plurality of switch cellscomprise n×m switch cells; said n×m switch cells being provided at n×mlattice positions on said principal surface; and said plurality ofswitch cells, said first and second mirrors, and said optical unit arearranged so that path lengths from said inputs to said outputs areequal.
 3. An optical switch having a plurality of switch cells, wherein:said optical switch has n inputs (n is a natural number) and m outputs(m is a natural number); said optical switch has a unit size defined asthe distance between any two adjacent ones of said switch cells; saidoptical switch comprises: a substrate having a switch size of K×L (K isan integer satisfying n≦K, and L is an integer satisfying m≦L), where Kand L represent a number of rows and a number of columns, respectively,of said optical switch; first and second mirrors parallel to each otherand perpendicular to a principal surface of said substrate; and anoptical unit providing a plurality of input optical paths for said ninputs and a plurality of output optical paths for said m outputs, saidplurality of input optical paths being inclined relative to said firstand second mirrors, said plurality of output optical paths beinginclined relative to said first and second mirrors; each of said switchcells comprises a switch mirror provided movably relative to saidsubstrate, wherein n=m=K=L; and said plurality of switch cells, saidfirst and second mirrors, and said optical unit are arranged so thatpath lengths from said inputs to said outputs are equal.
 4. An opticalswitch having a plurality of switch cells, wherein: said optical switchhas n inputs (n is a natural number) and m outputs (m is a naturalnumber); said optical switch has a unit size defined as the distancebetween any two adjacent ones of said switch cells; said optical switchcomprises: a substrate having a switch size of K×L (K is an integersatisfying n≦K, and L is an integer satisfying m≦L), where K and Lrepresent a number of rows and a number of columns, respectively, ofsaid optical switch; first and second mirrors parallel to each other andperpendicular to a principal surface of said substrate; and an opticalunit providing a plurality of input optical paths for said n inputs anda plurality of output optical paths for said m outputs, said pluralityof input optical paths being inclined relative to said first and secondmirrors, said plurality of output optical paths being inclined relativeto said first and second mirrors; each of said switch cells comprises aswitch mirror provided movably relative to said substrate, wherein saidplurality of input optical paths comprise odd-numbered channels andeven-numbered channels crossing each other, and said plurality of outputoptical paths comprise odd-numbered channels and even-numbered channelscrossing each other; and said plurality of switch cells, said first andsecond mirrors, and said optical unit are arranged so that path lengthsfrom said inputs to said outputs are equal.
 5. An optical switch havinga plurality of switch cells, wherein: said optical switch has n inputs(n is a natural number) and m outputs (m is a natural number); saidoptical switch has a unit size defined as the distance between any twoadjacent ones of said switch cells; said optical switch comprises: asubstrate having a switch size of K×L (K is an integer satisfying n≦K,and L is an integer satisfying m≦L), where K and L represent a number ofrows and a number of columns, respectively, of said optical switch;first and second mirrors parallel to each other and perpendicular to aprincipal surface of said substrate; and an optical unit providing aplurality of input optical paths for said n inputs and a plurality ofoutput optical paths for said m outputs, said plurality of input opticalpaths being inclined relative to said first and second mirrors, saidplurality of output optical paths being inclined relative to said firstand second mirrors; each of said switch cells comprises a switch mirrorprovided movably relative to said substrate, wherein said plurality ofinput optical paths are parallel to each other, and said plurality ofoutput optical paths are parallel to each other; and said plurality ofswitch cells, said first and second mirrors, and said optical unit arearranged so that path lengths from said inputs to said outputs areequal.
 6. An optical switch according to claim 5, wherein n ones of saidswitch cells connected to said n inputs are alternately inverted inlogic, and m ones of said switch cells connected to said m outputs arealternately inverted in logic.
 7. An optical switch according to claim5, wherein said plurality of switch cells comprise n first switch cellsconnected to said n inputs and at least (n²−1) second switch cellsprovided relatively near to said m outputs.
 8. An optical switchaccording to claim 7, wherein: each of said first switch cells switchesthe corresponding input optical path into between a first optical pathincluding reflection on said first mirror and a second optical path notincluding reflection on said first mirror; and each of said secondswitch cells is located so as to correspond to each of said first andsecond optical paths, and determines a final optical path reaching eachoutput.
 9. An optical switch according to claim 7, wherein: thepositions of said first switch cells are expressed in the form of (row,column) as (i, 1); i=1 to n; and the positions of said second switchcells are expressed in the form of (row, column) as: (n/2+i,2(n−1)−n/2+1−i); i=0 to (n−1) (n/2+i, 2(n−1)−n/2+2−i); i=0 to (n−1)(n/2+i+1, 2(n−1)−n/2+1−i); i=0 to (n−1) (n−1+i, 2(n−1)−i); i=0 to (n−1)(n+i, 2(n−1)−i); i=0 to (n−1).
 10. An optical switch according to claim7, wherein K=L=2(n−1).
 11. An optical switch according to claim 7,wherein K=L=2n−1.
 12. An optical switch according to claim 11, whereinsaid at least (n²−1) second switch cells become substantial when thenumber of said second switch cells are equal to or greater than n²,whereby said second mirror becomes unnecessary.
 13. An optical switchaccording to claim 7, wherein K=L=2n.
 14. An optical switch according toclaim 13, wherein said at least (n²−1) second switch cells becomesubstantial when the number of said second switch cells is equal to orgreater than n², whereby said second mirror becomes unnecessary.
 15. Anoptical switch according to claim 7, wherein said optical switch furthercomprises a plurality of lenses provided between said first switch cellsand said second switch cells.
 16. An optical switch according to claim15, wherein each of said plurality of lenses comprises a rod lens. 17.An optical switch according to claim 15, wherein said plurality oflenses comprise 2n lenses.
 18. An optical switch according to claim 15,wherein: n is less than 6; said principal surface of said substrate hasan excess space; and said plurality of lenses are provided in saidexcess space.
 19. An optical switch according to claim 15, wherein: n isgreater than 5; and said plurality of lenses are provided on saidprincipal surface of said substrate.
 20. An optical switch having aplurality of switch cells, wherein: said optical switch has n inputs (nis a natural number) and m outputs (m is a natural number); said opticalswitch has a unit size defined as the distance between any two adjacentones of said switch cells; said optical switch comprises: a substratehaving a switch size of K×L (K is an integer satisfying n≦K, and L is aninteger satisfying m≦L); first and second mirrors parallel to each otherand perpendicular to a principal surface of said substrate; and anoptical unit providing a plurality of input optical paths for said ninputs and a plurality of output optical paths for said m outputs, saidplurality of input optical paths being inclined relative to said firstand second mirrors, said plurality of output optical paths beinginclined relative to said first and second mirrors; and each of saidswitch cells comprises a switch mirror provided movably relative to saidsubstrate, wherein: n=m=K, L=n+1, and n is an even number; K and Lrepresent a number of rows and a number of columns, respectively, ofsaid optical switch; said optical switch further comprises n lensesprovided in the (n/2+1)-th column; and said plurality of switch cells,said first and second mirrors, and said optical unit are arranged sothat path lengths from said inputs to said outputs are equal.
 21. Anoptical switch according to claim 20, wherein each of said n lensescomprises a spherical lens.
 22. An optical switch having a plurality ofswitch cells, wherein: said optical switch has n inputs (n is a naturalnumber) and m outputs (m is a natural number); said optical switch has aunit size defined as the distance between any two adjacent ones of saidswitch cells; said optical switch comprises: a substrate having a switchsize of K×L (K is an integer satisfying n≦K, and L is an integersatisfying m≦L); first and second mirrors parallel to each other andperpendicular to a principal surface of said substrate; and an opticalunit providing a plurality of input optical paths for said n inputs anda plurality of output optical paths for said m outputs, said pluralityof input optical paths being inclined relative to said first and secondmirrors, said plurality of output optical paths being inclined relativeto said first and second mirrors; and each of said switch cellscomprises a switch mirror provided movably relative to said substrate,wherein: n=m=K, L=n+1, and n is an odd number; K and L represent anumber of rows and a number of columns, respectively, of said opticalswitch; said optical switch further comprises n lenses provided in the[(n+1)/2+1]-th column; and said plurality of switch cells, said firstand second mirrors, and said optical unit are arranged so that pathlengths from said inputs to said outputs are equal.
 23. An opticalswitch according to claim 22, wherein each of said n lenses comprises aspherical lens.
 24. An optical switch having a plurality of switchcells, wherein: said optical switch has n inputs (n is a natural number)and m outputs (m is a natural number); said optical switch has a unitsize defined as the distance between any two adjacent ones of saidswitch cells; said optical switch comprises: a substrate having a switchsize of K×L (K is an integer satisfying n≦K, and L is an integersatisfying m≦L); first and second mirrors parallel to each other andperpendicular to a principal surface of said substrate; and an opticalunit providing a plurality of input optical paths for said n inputs anda plurality of output optical paths for said m outputs, said pluralityof input optical paths being inclined relative to said first and secondmirrors, said plurality of output optical paths being inclined relativeto said first and second mirrors; and each of said switch cellscomprises a switch mirror provided movably relative to said substrate,wherein: n=m=K, and L=n+1; K and L represent a number of rows and anumber of columns, respectively, of said optical switch; said opticalswitch further comprises n lenses provided in an arbitrary one of saidcolumns; and said plurality of switch cells, said first and secondmirrors, and said optical unit are arranged so that path lengths fromsaid inputs to said outputs are equal.
 25. An optical switch having aplurality of switch cells, wherein: said optical switch has n inputs (nis a natural number) and m outputs (m is a natural number); said opticalswitch has a unit size defined as the distance between any two adjacentones of said switch cells; said optical switch comprises: a substratehaving a switch size of K×L (K is an integer satisfying n≦K, and L is aninteger satisfying m≦L), where K and L represent a number of rows and anumber of columns, respectively, of said optical switch; first andsecond mirrors parallel to each other and perpendicular to a principalsurface of said substrate; and an optical unit providing a plurality ofinput optical paths for said n inputs and a plurality of output opticalpaths for said m outputs, said plurality of input optical paths beinginclined relative to said first and second mirrors, said plurality ofoutput optical paths being inclined relative to said first and secondmirrors; and each of said switch cells comprises a switch mirrorprovided movably relative to said substrate, wherein: n=m, K=n+1, andL=n+2; said optical switch further comprises 2n lenses providedsubstantially along a diagonal line of said principal surface; and saidplurality of switch cells, said first and second mirrors, and saidoptical unit are arranged so that path lengths from said inputs to saidoutputs are equal.
 26. An optical switch according to claim 25, whereineach of said 2n lenses comprises a rod lens.
 27. An optical switchhaving a plurality of switch cells, wherein: said optical switch has ninputs (n is a natural number) and m outputs (m is a natural number);said optical switch has a unit size defined as the distance between anytwo adjacent ones of said switch cells; said optical switch comprises: asubstrate having a switch size of K×L (K is an integer satisfying n≦K,and L is an integer satisfying m≦L), where K and L represent a number ofrows and a number of columns, respectively, of said optical switch;first and second mirrors parallel to each other and perpendicular to aprincipal surface of said substrate; and an optical unit providing aplurality of input optical paths for said n inputs and a plurality ofoutput optical paths for said m outputs, said plurality of input opticalpaths being inclined relative to said first and second mirrors, saidplurality of output optical paths being inclined relative to said firstand second mirrors; and each of said switch cells comprises a switchmirror provided movably relative to said substrate, wherein:K=L=n+1=m+1; said plurality of switch cells are provided at (n+1)×(n+1)lattice positions on said principal surface of said substrate; and saidplurality of switch cells, said first and second mirrors, and saidoptical unit are arranged so that path lengths from said inputs to saidoutputs are equal.
 28. An optical switch according to claim 27, wherein:said plurality of switch cells comprise first switch cells and secondswitch cells; said switch mirror in each of said first switch cells isoriented in a first direction; and said switch mirror in each of saidsecond switch cells is oriented in a second direction opposite to saidfirst direction.
 29. An optical switch according to claim 28, whereinsaid optical switch further comprises a plurality of lenses providedbetween said first switch cells and said second switch cells.
 30. Anoptical switch according to claim 29, wherein each of said lenses is arod lens.
 31. An optical switch having a plurality of switch cells,wherein: said optical switch has n inputs (n is a natural number) and moutputs (m is a natural number); said optical switch has a unit sizedefined as the distance between any two adjacent ones of said switchcells; said optical switch comprises: a substrate having a switch sizeof K×L (K is an integer satisfying n≦K, and L is an integer satisfyingm≦L), where K and L represent a number of rows and a number of columns,respectively, of said optical switch; first and second mirrors parallelto each other and perpendicular to a principal surface of saidsubstrate; and an optical unit providing a plurality of input opticalpaths for said n inputs and a plurality of output optical paths for saidm outputs, said plurality of input optical paths being inclined relativeto said first and second mirrors, said plurality of output optical pathsbeing inclined relative to said first and second mirrors; and each ofsaid switch cells comprises a switch mirror provided movably relative tosaid substrate, wherein said optical switch further comprises a lensprovided on said substrate, and said plurality of switch cells, saidfirst and second mirrors, and said optical unit are arranged so thatoath lengths from said inputs to said outputs are equal.
 32. An opticalswitch having a plurality of switch cells, wherein: said optical switchhas n inputs (n is a natural number) and m outputs (m is a naturalnumber); said optical switch has a unit size defined as the distancebetween any two adjacent ones of said switch cells; said optical switchcomprises: a substrate having a switch size of K×L (K is an integersatisfying n≦K, and L is an integer satisfying m≦L), where K and Lrepresent a number of rows and a number of columns, respectively, ofsaid optical switch; first and second mirrors parallel to each other andperpendicular to a principal surface of said substrate; and an opticalunit providing a plurality of input optical paths for said n inputs anda plurality of output optical paths for said m outputs, said pluralityof input optical paths being inclined relative to said first and secondmirrors, said plurality of output optical paths being inclined relativeto said first and second mirrors; each of said switch cells comprises aswitch mirror provided movably relative to said substrate, wherein n=m;and said plurality of switch cells, said first and second mirrors, andsaid optical unit are arranged so that path lengths from said inputs tosaid outputs are equal.